J/ApJ/772/107 Giant molecular clouds in nearby galaxies (Donovan Meyer+, 2013)
Resolved giant molecular clouds in nearby spiral galaxies: insights from
the CANON CO (1-0) survey.
Donovan Meyer J., Koda J., Momose R., Mooney T., Egusa F., Carty M.,
Kennicutt R., Kuno N., Rebolledo D., Sawada T., Scoville N., Wong T.
<Astrophys. J., 772, 107 (2013)>
=2013ApJ...772..107D 2013ApJ...772..107D
ADC_Keywords: Galaxies, nearby ; Molecular clouds ; Radio lines ;
Velocity dispersion
Keywords: galaxies: individual (NGC 2403, NGC 3031, NGC 4736, NGC 4826,
NGC 6946); galaxies: ISM; ISM: molecules
Abstract:
We resolve 182 individual giant molecular clouds (GMCs) larger than
2.5x105M☉ in the inner disks of 5 large nearby spiral galaxies
(NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the
largest such sample of extragalactic GMCs within galaxies analogous to
the Milky Way. Using a conservatively chosen sample of GMCs most
likely to adhere to the virial assumption, we measure cloud sizes,
velocity dispersions, and 12CO(J=1-0) luminosities and calculate
cloud virial masses. The average conversion factor from CO flux to
H2 mass (or XCO) for each galaxy is 1-2x1020/cm2 (K.km/s)-1,
all within a factor of two of the Milky Way disk value
(∼2x1020/cm2(K.km/s)-1). We find GMCs to be generally consistent
within our errors between the galaxies and with Milky Way disk GMCs;
the intrinsic scatter between clouds is of order a factor of two.
Consistent with previous studies in the Local Group, we find a linear
relationship between cloud virial mass and CO luminosity, supporting
the assumption that the clouds in this GMC sample are gravitationally
bound. We do not detect a significant population of GMCs with elevated
velocity dispersions for their sizes, as has been detected in the
Galactic center. Though the range of metallicities probed in this
study is narrow, the average conversion factors of these galaxies will
serve to anchor the high metallicity end of metallicity-XCO trends
measured using conversion factors in resolved clouds; this has been
previously possible primarily with Milky Way measurements.
Description:
The CO(J=1-0) observations presented in this paper were taken as part
of the CANON CO(1-0) Survey, in which data from the Combined Array for
Research in Millimeter Astronomy (CARMA) and Nobeyama Radio
Observatory 45m (NRO45) single dish telescope are combined to image
the central regions of nearby spiral galaxies (J. Koda et al., in
preparation).
We observe all galaxies in the (J=1-0) transition of 12CO with CARMA
in the C and D configurations. The observations presented in this
paper were taken from early 2007 through 2012 March.
To achieve accurate total flux measurements, we also observe the
galaxies using the Beam Array Receiver System (BEARS) instrument on
the NRO45 single dish telescope. The total bandwidth is 265MHz, and we
smooth the 500kHz velocity resolution to 5.08km/s to match the CARMA
data.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 75 5 Galaxy properties
table3.dat 71 182 Giant molecular cloud (GMC) properties
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See also:
J/A+A/560/A24 : IRAM 30m CO-observations in W43 (Carlhoff+, 2013)
J/ApJ/761/37 : CO obs. in giant molecular clouds of M33 (Miura+, 2012)
J/ApJS/190/233 : Spectroscopy & abundances of SINGS galaxies (Moustakas+, 2010)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)
J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008)
J/ApJ/654/240 : Giant molecular clouds in M31 (Rosolowsky+, 2007)
J/ApJ/617/240 : Oxygen abundances in the GOODS-North field (Kobulnicky+, 2004)
J/ApJS/149/343 : Giant molecular clouds in M33 (Engargiola+, 2003)
J/ApJS/144/47 : Outer galaxy molecular cloud catalog (Brunt+, 2003)
J/PASJ/53/971 : CO catalog of LMC molecular clouds (Mizuno+, 2001)
J/ApJ/428/693 : Rosette Nebula and Maddalena Cloud structures (Williams+ 1994)
J/ApJS/63/821 : Inner Galaxy Molecular clouds & cloud cores (Scoville+, 1987)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I4 --- NGC NGC number
10- 11 I2 h RAh NED Hour of right ascension (J2000)
13- 14 I2 min RAm Minute of right ascension (J2000)
16- 19 F4.1 s RAs Second of right ascension (J2000)
21 A1 --- DE- NED Sign of declination (J2000)
22- 23 I2 deg DEd NED Degree of declination (J2000)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 29 I2 arcsec DEs Arcsecond of declination (J2000)
31- 33 I3 km/s Vel [-34/408] NED optical velocity
35- 38 F4.2 Mpc Dist [3.1/7.5] Distance (1)
40- 43 F4.2 Mpc e_Dist Dist uncertainty (1)
45- 49 A5 --- MType Morphological type
51- 52 I2 deg Inc [32/60] Inclination angle (1)
54- 57 F4.2 [-] Met [8.9/9.2] Central metallicity 12+log(O/H) (1)
59- 62 F4.2 [-] e_Met Met uncertainty (1)
63 A1 --- f_Met [a] Flag on Met (2)
65- 69 F5.2 --- Grad ? Metallicity gradient (dex/ρ25) (1)
71- 75 F5.2 arcmin rho25 Radius of the major axis at the
µB=25mag/arcsec2 isophote (1)
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Note (1): Distances, inclination angles, metallicities, and ρ25 are from
Moustakas et al. (2010, J/ApJS/190/233). The metallicities utilize
the Kobulnicky & Kewley (2004, J/ApJ/617/240) calibration.
Note (2):
a = As discussed in Section 7, we refer to the characteristic metallicity of
NGC 4736 (9.01±0.03; Moustakas et al. 2010, J/ApJS/190/233) in
Figure 8 instead of this central value.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [NGC]
4- 7 I4 --- NGC Galaxy NGC number
8 A1 --- --- [-]
9- 10 I2 --- Seq [1/87] GMC number
12- 20 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
22- 30 F9.6 deg DEdeg Declination in decimal degrees (J2000)
32- 36 F5.1 pc Rad [36/233] Radius (1)
38- 42 F5.2 km/s sigma [2.6/21] Velocity dispersion (1)
44- 50 F7.3 K.km/s.pc2 Lum [0.9/340] CO luminosity
52- 57 F6.2 Msun Mass [2.7/761] Virial mass
59- 63 F5.3 cm-2/(K.km/s) XCO Conversion factor; cm-2/(K km/s)
65 A1 --- Arm Arm class estimate (1=spiral arm;
2=interarm region)
67- 71 F5.2 --- S/N [3.4/22] Signal-to-Noise
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Note (1): The uncertainties in size and velocity dispersion are assumed to be
25% of the spatial beam size (15-19.5pc) and half of the unsmoothed
velocity channel width (1.3km/s). As discussed in Section 4.3, the
upper limit to the uncertainties for the smallest clouds is half of
the spatial beam size (30-39pc) and 2.6km/s.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 04-Feb-2015